1. Field
The invention relates to methods, equipment and software products for fault tolerant Internet Protocol (IP) service.
2. Description of the Related Art
Voice over Internet Protocol (VoIP) service relates to transmission of voice traffic in data packets in a network supporting Internet Protocol (IP). When the present invention is made, state of the art in VoIP service was defined in Internet standards RFC3550: A Transport Protocol for Real-Time Applications (“RTP”); RFC2543, RFC3261: A Session Initiation Protocol (“SIP”); RFC2327: Session Description Protocol (“SDP”); RFC3264: An Offer/Answer Model with the Session Description Protocol (“SDP”); RFC3515: The Session Initiation Protocol (“SIP”) Refer Method; and RFC 3265: Session Initiation Protocol (“SIP”)-Specific Event Notification. It is to be noted, however, the VoIP development is an ongoing process, and the invention is equally applicable to future VoIP developments.
A key element in VoIP service is Session Initiation Protocol Server, or SIP server. The SIP protocol operates with user agents and user agent servers. The server's task is to provide name-to-address resolution and location management in respect of the user. Other services which are essential to full operation of VoIP service network include Dynamic Host Configuration Protocol (DHCP) which is a client-server networking protocol. A DHCP server provides configuration parameters specific to the DHCP client host requesting, generally, information required by the client host to participate on an IP network. DHCP also provides a mechanism for allocation of IP addresses to client hosts.
A VoIP service network comprises terminals and local-area network (LAN) switches and/or hubs, which may be integrated to the terminal functionality. A VoIP service network may implement point-to-point and group/conference calls.
A problem arises when one or more of the VoIP servers are out of service. For instance, absence of the SIP server makes conventional group calls impossible. Absence of the DHCP server is an even worse problem, which would result in total loss of communication as terminals are unable to resolve IP addresses. Use of static IP addresses is generally impractical in real-world networks with large numbers of roaming terminals.
While the above description of problems of prior art networks relate to VoIP traffic, those skilled in the art will realize that similar problems affect other types of communication, such as data traffic.